Heat pump with restorative operation for magneto caloric material

ABSTRACT

A heat pump system is provided that uses MCM to provide for heating or cooling. The heat pump can include one or more stages of MCM, each stage having an original peak Curie temperature. In the event the magneto caloric response of one or more stages of MCM degrades, the present invention provides for operating the heat pump system so that one or more stages of MCM are held at a different temperature from the original peak Curie temperature so as to restore the MCM to its original peak Curie temperature or to within a certain interval thereof. The present invention can be used with e.g., an appliance, air-conditioning systems (heating or cooling), or other devices using such a heat pump system as well.

FIELD OF THE INVENTION

The subject matter of the present disclosure relates generally to a heatpump that uses magneto caloric material to provide for heat transfer.

BACKGROUND OF THE INVENTION

Conventional refrigeration technology typically utilizes a heat pumpthat relies on compression and expansion of a fluid refrigerant toreceive and reject heat in a cyclic manner so as to effect a desiredtemperature change or i.e. transfer heat energy from one location toanother. This cycle can be used to provide e.g., for the receiving ofheat from a refrigeration compartment and the rejecting of such heat tothe environment or a location that is external to the compartment. Otherapplications include air conditioning of residential or commercialstructures. A variety of different fluid refrigerants have beendeveloped that can be used with a heat pump in such systems.

Certain challenges exist with these conventional heat pump systems.While improvements have been made, at best heat pump systems that relyon the compression of fluid refrigerant can still only operate at about45 percent or less of the maximum theoretical Carnot cycle efficiency.Also, some fluid refrigerants have been discontinued due toenvironmental concerns. The range of ambient temperatures over whichcertain such refrigerant-based systems can operate may be impracticalfor certain locations. Other challenges with heat pumps that use a fluidrefrigerant exist as well.

Magneto caloric material (MCM)—i.e. a material that exhibits the magnetocaloric effect—provides a potential alternative to fluid refrigerantsfor heat pump applications. In general, the magnetic moments of a normalMCM will become more ordered under an increasing, externally appliedmagnetic field and cause the MCM to generate heat. Conversely,decreasing the externally applied magnetic field will allow the magneticmoments of the MCM to become more disordered and allow the MCM to absorbheat. Some MCM types exhibit the opposite behavior—i.e. generating heatwhen a magnetic field is removed and becoming cooler when placed intothe magnetic field. This latter type can be referred to as inverse orpara-magneto caloric material. Both normal and inverse MCM are referredto collectively herein as magneto caloric material or MCM. Thetheoretical Carnot cycle efficiency of a refrigeration cycle based on anMCM can be significantly higher than for a comparable refrigerationcycle based on a fluid refrigerant. As such, a heat pump system that caneffectively use an MCM would be useful.

Challenges exist to the practical and cost competitive use of an MCM,however. In addition to the development of suitable types of MCM,equipment that can attractively utilize an MCM is still needed.Additionally, as stated above, the ambient conditions under which a heatpump may be needed can vary substantially. For example, for arefrigerator appliance placed in a garage or located in a non-airconditioned space, ambient temperatures can range from below freezing toover 90° F. Some types of MCM are capable of accepting and generatingheat only within a much narrower temperature range than presented bysuch ambient conditions. Also, different MCM types may exhibit themagneto caloric effect more prominently at different temperatures.

Another issue is that some MCM types undesirably degrade with use. Moreparticularly, certain types of MCM will undergo a gradual change ordegradation in their magneto caloric response (also referred to as “agesplitting”). Such degradation causes the temperature at which these MCMsexhibit the magneto caloric response, referred to as the Curietemperature, to change after extended periods of use near or at theoriginal Curie temperature. The change can become significant,precluding the proper functioning of the MCM and a heat pump in which itis incorporated.

Accordingly, a heat pump system that can address certain challengesincluding those identified above would be useful. Particularly, a heatpump that can be operated so as to restore MCM that has undergonedegradation of its magnetic caloric response at the original Curietemperature would be useful.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a heat pump system that uses MCM toprovide for heating or cooling. The heat pump can include one or morestages of MCM, each stage having an original peak Curie temperature. Inthe event the magneto caloric response of one or more stages of MCMdegrades, the present invention provides for operating the heat pumpsystem so that one or more stages of MCM are held at a differenttemperature from the original peak Curie temperature so as to restorethe MCM to its original peak Curie temperature or to within a certaininterval thereof. The present invention can be used with e.g., anappliance, air-conditioning systems (heating or cooling), or otherdevices using such a heat pump system as well. Additional aspects andadvantages of the invention will be set forth in part in the followingdescription, or may be apparent from the description, or may be learnedthrough practice of the invention.

In one exemplary embodiment, the present invention provides a method ofoperating a heat pump system. The heat pump system includes a heattransfer fluid, a first heat exchanger, a second heat exchanger, andmagneto caloric material having an original Curie temperature range,ΔT_(OC). The steps of the method include circulating a heat transferfluid through the first heat exchanger, the second heat exchanger, andthe magneto caloric material; causing a change in Curie temperaturerange of the magneto caloric material away from the original Curietemperature range ΔT_(OC); reducing the rate of flow of the heattransfer fluid from a normal operating flow rate; exchanging heat energywith the magneto caloric material during the step of reducing; andrestoring the magneto caloric material to the original Curie temperaturerange ΔT_(OC) during the step of exchanging.

In another exemplary aspect, the present invention provides a method ofoperating a heat pump system. The heat pump system includes a heattransfer fluid, a first heat exchanger, a second heat exchanger, and aworking unit that includes a plurality of adjacent stages of magnetocaloric materials through which the heat transfer fluid flowssequentially. The magneto caloric material of each stage has an originalCurie temperature range ΔT_(OC) that includes an original peak Curietemperature, T_(OC). The steps of the method include circulating a heattransfer fluid through the first heat exchanger, a second heatexchanger, and the plurality of adjacent stages of magneto caloricmaterials; shifting the Curie temperature range of the magneto caloricmaterial of at least one stage away from the original Curie temperaturerange ΔT_(OC); reducing the rate of flow of the heat transfer fluid froma normal operating flow rate; exchanging heat energy between the heattransfer fluid and the magneto caloric material during the step ofreducing; and restoring the magneto caloric material of the at least onestage to the original Curie temperature range ΔT_(OC) during the step ofexchanging.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendedfigures, in which:

FIG. 1 provides an exemplary embodiment of a refrigerator appliance ofthe present invention.

FIG. 2 is a schematic illustration of an exemplary heat pump system ofthe present invention positioned in an exemplary refrigerator with amachinery compartment and at least one refrigerated compartment.

FIG. 3 provides a perspective view of an exemplary heat pump of thepresent invention.

FIG. 4 is an exploded view of the exemplary heat pump of FIG. 3.

FIG. 5 is a cross-sectional view of the exemplary heat pump of FIG. 3.

FIG. 6 is perspective view of the exemplary heat pump of FIG. 3. Valveslocated at the ends of a regenerator housing have been removed forpurposes of further explanation of this exemplary embodiment of theinvention as set forth below.

FIG. 7 is a perspective and exploded view of a plate and seal at one endof the heat pump of FIG. 3.

FIG. 8 is a schematic representation of an exemplary method of operatinga heat pump of the present invention.

FIGS. 9, 10, 11, 12, and 13 provide plots of the temperature response ofone or more stages of MCM as further described below.

FIG. 14 is a plot of certain data regarding several stages of MCM asfurther described below.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

Referring now to FIG. 1, an exemplary embodiment of a refrigeratorappliance 10 is depicted as an upright refrigerator having a cabinet orcasing 12 that defines a number of internal storage compartments orchilled chambers. In particular, refrigerator appliance 10 includesupper fresh-food compartments 14 having doors 16 and lower freezercompartment 18 having upper drawer 20 and lower drawer 22. The drawers20, 22 are “pull-out” type drawers in that they can be manually movedinto and out of the freezer compartment 18 on suitable slide mechanisms.

Refrigerator 10 is provided by way of example only. Other configurationsfor a refrigerator appliance may be used as well including applianceswith only freezer compartments, only chilled compartments, or othercombinations thereof different from that shown in FIG. 1. In addition,the heat pump and heat pump system of the present invention is notlimited to appliances and may be used in other applications as well suchas e.g., air-conditioning, electronics cooling devices, and others.Thus, it should be understood that while the use of a heat pump toprovide cooling within a refrigerator is provided by way of exampleherein, the present invention may also be used in other applications toprovide for heating and/or cooling as well.

FIG. 2 is a schematic view of another exemplary embodiment of arefrigerator appliance 10 including a refrigeration compartment 30 and amachinery compartment 40. In particular, machinery compartment 30includes an exemplary heat pump system 52 of the present inventionhaving a first heat exchanger 32 positioned in the refrigerationcompartment 30 for the removal of heat therefrom. A heat transfer fluidsuch as e.g., an aqueous solution, flowing within first heat exchanger32 receives heat from the refrigeration compartment 30 thereby coolingits contents. A fan 38 may be used to provide for a flow of air acrossfirst heat exchanger 32 to improve the rate of heat transfer from therefrigeration compartment 30.

The heat transfer fluid flows out of first heat exchanger 32 by line 44to heat pump 100. As will be further described herein, the heat transferfluid receives additional heat associated with the magneto caloriceffect provided by MCM in heat pump 100 and carries this heat by line 48to pump 42 and then to second heat exchanger 34. Heat is released to theenvironment, machinery compartment 40, and/or another location externalto refrigeration compartment 30 using second heat exchanger 34. A fan 36may be used to create a flow of air across second heat exchanger 34 andthereby improve the rate of heat transfer to the environment. Pump 42connected into line 48 causes the heat transfer fluid to recirculate inheat pump system 52. Motor 28 is in mechanical communication with heatpump 100 as will be further described.

From second heat exchanger 34 the heat transfer fluid returns by line 50to heat pump 100 where, as will be further described below, due to themagneto caloric effect, the heat transfer fluid loses heat to the MCM inheat pump 100. The now colder heat transfer fluid flows by line 46 tofirst heat exchanger 32 to receive heat from refrigeration compartment30 and repeat the cycle as just described.

Heat pump system 52 is provided by way of example only. Otherconfigurations of heat pump system 52 may be used as well. For example,lines 44, 46, 48, and 50 provide fluid communication between the variouscomponents of the heat pump system 52 but other heat transfer fluidrecirculation loops with different lines and connections may also beemployed. Valves can be placed in one or more of lines 44, 46, 48, and50 to e.g., control flow and may communicate with a controller (nowshown) configured for operating heat pump system 52 according to certainexemplary aspects of the present invention. Additionally, pump 42 canalso be positioned at other locations or on other lines in system 52.Pump 42 may be e.g., a variable speed pump operated by a controlleraccording to certain exemplary aspects of the present invention. Stillother configurations of heat pump system 52 may be used as well. Heatpump system 52 could also be configured with e.g., air-conditioningsystems and other applications in addition to a refrigeration appliance.

FIGS. 3, 4, 5, and 6 depict various views of an exemplary heat pump 100of the present invention. Heat pump 100 includes a regenerator housing102 that extends longitudinally along an axial direction between a firstend 118 and a second end 120. The axial direction is defined by axis A-Aabout which regenerator housing 102 rotates. A radial direction R isdefined by a radius extending orthogonally from the axis of rotation A-A(FIG. 5). A circumferential direction is indicated by arrows C.

Regenerator housing 102 defines a plurality of chambers 104 that extendlongitudinally along the axial direction defined by axis A-A. Chambers104 are positioned proximate or adjacent to each other alongcircumferential direction C. Each chamber 104 includes a pair ofopenings 106 and 108 positioned at opposing ends 118 and 120 ofregenerator housing 102 (FIG. 4).

For this exemplary embodiment, heat pump 100 also includes a pluralityof working units 112 that each include MCM. Each working unit 112 islocated in one of the chambers 104 and extends along axial directionA-A. For the exemplary embodiment shown in the figures, heat pump 100includes eight working units 112 positioned adjacent to each other alongthe circumferential direction as shown and extending longitudinallyalong the axial direction A-A. As will be understood by one of skill inthe art using the teachings disclosed herein, a different number ofworking units 112 other than eight may be used as well. For example, 2,4, 6, 12, and other numbers of working units (and associated chambers)may also be used.

As will be understood using the teachings disclosed herein, the presentinvention is not limited to a regenerator housing 102 having thestructure shown in FIG. 4. Instead, other configurations may be used forcreating multiple working units 112. For example, regenerator housing102 can be provided without chambers 104 for each working unit 112. Insuch an embodiment, the working units 112 would be defined by the MCM.For example, the working units 112 could be partitioned alongcircumferential direction C by multiple spaces dividing the MCM intoworking units 122 instead of being partitioned by the walls definingchambers 104. In still another embodiment, MCM could be provided havingchannels, grooves, or other features dividing the MCM along thecircumferential direction C into multiple working units. Otherconfigurations where regenerator housing 102 does not include structuresuch as chambers 104 for partitioning the MCM into the various workingunits 112 could be used as well.

A pair of valves 113 and 115 are positioned at axial ends of regeneratorhousing 102 (FIG. 4). Together valves 113 and 115 include a pair ofrotatable plates 114 and 116, a pair of fixed plates 121 and 123, andpair of gaskets 117 and 119. As will be further described, gaskets 117and 119 are configured to provide fluids seals between the pair ofrotatable plates 114, 116 and the pair of fixed plates 121, 123,respectively.

First rotatable plate 114 is attached to first end 118 and secondrotatable plate 116 is attached to second end 120. As shown in FIG. 4and FIG. 7 (only rotatable plate 114 is shown in FIG. 7—plate 116 wouldbe substantially identical in construction), each rotatable plate 114and 116 includes a plurality of apertures 122 and 124, respectively. Forthis exemplary embodiment, apertures 122 and 124 are configured ascircumferentially-extending slots that are spaced apart alongcircumferential direction C.

Using rotatable plate 114 by way of example, gasket 117 is received intoa recess 131 defined by plate 114. A plurality of projections 129 extendfrom plate 114 along axial direction A towards fixed plate 121 anddefine apertures 122. Gasket 117 defines a plurality of channels 125 inwhich projections 129 are received. As such, channels 125 andprojections 129 help secure the position of gasket 117 relative torotatable plate 114 by preventing gasket 117 from rotating relative toplate 114 during operation of the heat pump. For this exemplaryembodiment, the opposing faces 133 and 135 of gasket 117 contact fixedplate 121 and rotatable plate 114, respectively, to form a fluid tightseal therebetween. During operation, as regenerator housing 102 rotatesabout axis A-A, gasket 117 rotates with rotatable plate 114 and alsoslides over the inside face 137 (FIG. 4) of fixed plate 121 whilemaintaining the fluid seal. A similar construction and operation is usedfor fixed plate 123 with inside face 139, gasket 119 with opposing faces141 and 143, and rotatable plate 116. The plurality of apertures 122 and124 of the first and second rotatable plates 114 and 116 are alignedwith the plurality of apertures 125 and 127 of the pair of gaskets 117and 119 so as to provide fluid communication therebetween.

A variety of constructions may be used for gaskets 117 and 119. Forexample, gaskets 117,119 could be constructed from a homogenous materialor could be constructed from layers and/or segments of differentmaterials. Gaskets 117, 119 could be a unitary part as shown or could beformed from multiple parts. Also, gaskets 117 and 119 could be formedfrom one or more materials deposited, adhered, or layered onto e.g.,plates 114,116. For example, gaskets 117 and 119 could be formed ascoatings on plates 114, 116. Gaskets 117 and 119 could be formed fromelastomeric or other pliable materials. Other constructions may be usedas well.

Each aperture 122 is positioned adjacent to a respective opening 106 ofa chamber 104. Each aperture 124 is positioned adjacent to a respectiveopening 108 of a chamber 104. Accordingly, a heat transfer fluid mayflow into a chamber 104 through a respective aperture 122 and opening106 so as to flow through the MCM in a respective working unit 112 andthen exit through opening 108 and aperture 124. A reverse path can beused for flow of the heat transfer fluid in the opposite directionthrough the working unit 112 of a given chamber 104.

Referring to FIG. 4, first fixed plate 121 has a first inlet port 140and a first outlet port 142 and is positioned adjacent to rotatableplate 114. As shown, ports 140 and 142 are positioned 180 degrees apartabout the circumferential direction C of first seal 114. However, otherconfigurations may be used. For example, ports 140 and 142 may bepositioned within a range of about 170 degrees to about 190 degreesabout the circumferential direction C as well. Rotatable plate 114 andregenerator housing 102 are rotatable relative to first fixed plate 121.Ports 140 and 142 are connected with lines 44 and 46 (FIG. 1),respectively. As such, the rotation of regenerator housing 102 aboutaxis A-A sequentially places lines 44 and 46 in fluid communication withat least two working units 112 of MCM at any one time as will be furtherdescribed.

Second fixed plate 123 has a second inlet port 144 and a second outletport 146 and is positioned adjacent to second rotatable plate 116. Asshown, ports 144 and 146 are positioned 180 degrees apart about thecircumferential direction C of second seal 116. However, otherconfigurations may be used. For example, ports 144 and 146 may bepositioned within a range of about 170 degrees to about 190 degreesabout the circumferential direction C as well. Second rotatable plate116 and regenerator housing 102 are rotatable relative to second fixedplate 123. Ports 144 and 146 are connected with lines 50 and 48 (FIG.1), respectively. As such, the rotation of regenerator housing 102 aboutaxis A-A sequentially places lines 48 and 50 in fluid communication withat least two working units 112 of MCM at any one time as will be furtherdescribed. Notably, at any one time during rotation of regeneratorhousing 102, lines 46 and 50 will each be in fluid communication with atleast one working unit 112 while lines 44 and 48 will also be in fluidcommunication with at least one other working unit 112 located about 180degrees away along the circumferential direction.

As shown in FIGS. 4, 5, and 6, regenerator housing 102 defines a cavity128 that is positioned radially inward of the plurality of chambers 104and extends along the axial direction between first end 118 and secondend 120. A magnetic device 126 is positioned within cavity 128 and, forthis exemplary embodiment, extends along the axial direction betweenfirst end 118 and second end 120. Magnetic device 126 provides amagnetic field M that is directed radially outward as indicated byarrows M in FIG. 5.

The positioning and configuration of magnetic device 126 is such thatonly a subset (e.g., one, two, or more) of the plurality of workingunits 112 is/are within or subjected to magnetic field M at any onetime. For example, as shown in FIG. 5, working units 112 a and 112 e arepartially within the magnetic field while units 112 b, 112 c, and 112 dare fully within the magnetic field M created by magnetic device 126.Conversely, the magnetic device 126 is configured and positioned so thatworking units 112 f, 112 g, and 112 h are completely or substantiallyout of the magnetic field created by magnetic device 126. However, asregenerator housing 102 is continuously rotated along circumferentialdirection C as shown by arrow W, the subset of working units 112 withinthe magnetic field will continuously change as some working units 112will enter magnetic field M and others will exit.

FIG. 8 illustrates an exemplary method of the present invention using aschematic representation of a working unit 112 of MCM in regeneratorhousing 102 as it rotates in the direction of arrow W between positions1 through 8 as shown in FIG. 6. During step 200, working unit 112 isfully within magnetic field M, which causes the magnetic moments of thematerial to orient and the MCM to heat (when a normal MCM is used) aspart of the magneto caloric effect. Ordering of the magnetic field iscreated and maintained as working unit 112 is rotated sequentiallythrough positions 2, 3, and then 4 (FIG. 6) as regenerator housing 102is rotated in the direction of arrow W. During the time at positions 2,3, and 4, the heat transfer fluid dwells in the MCM of working unit 112and, therefore, is heated. More specifically, the heat transfer fluiddoes not flow through working unit 112 because the openings 106,108,122, and 124 corresponding to working unit 112 in positions 2, 3, and 4are not aligned with any of the ports 140, 142, 144, or 146.

In step 202, as regenerator housing 102 continues to rotate in thedirection of arrow W, working unit 112 will eventually reach position 5.As shown in FIGS. 3 and 6, at position 5 the heat transfer fluid canflow through the MCM as first inlet port 140 is now aligned with anopening 122 in first valve 114 and an opening 106 at the first end 118of working unit 112 while second outlet port 146 is aligned with anopening 124 in second valve 116 at the second end 120 of working unit112.

As indicated by arrow Q_(H-OUT) in FIGS. 3 and 8, heat transfer fluid inworking unit 112, now heated by the MCM, can travel out of regeneratorhousing 102 and along line 48 to the second heat exchanger 34. At thesame time, and as indicated by arrow Q_(H-IN), heat transfer fluid fromfirst heat exchanger 32 flows into working unit 112 from line 44 whenworking unit 112 is at position 5. Because heat transfer fluid from thefirst heat exchanger 32 is relatively cooler than the MCM in workingunit 112, the MCM will lose heat to the heat transfer fluid.

Referring again to FIG. 8 and step 204, as regenerator housing 102continues to rotate in the direction of arrow W, working unit 112 ismoved sequentially through positions 6, 7, and 8 where working unit 112is completely or substantially out of magnetic field M. The absence orlessening of the magnetic field is such that the magnetic moments of theMCM become disordered and the MCM absorbs heat as part of the magnetocaloric effect for a normal MCM. During the time in positions 6, 7, and8, the heat transfer fluid dwells in the MCM of working unit 112 and,therefore, is cooled by losing heat to the MCM as the magnetic momentsdisorder. More specifically, the heat transfer fluid does not flowthrough working unit 112 because the openings 106, 108, 122, and 124corresponding to working unit 112 when in positions 6, 7, and 8 are notaligned with any of the ports 140, 142, 144, or 146.

Referring to step 206 of FIG. 8, as regenerator housing 102 continues torotate in the direction of arrow W, working unit 112 will eventuallyreach position 1. As shown in FIGS. 3 and 6, at position 1 the heattransfer fluid in working unit 112 can flow through the MCM as secondinlet port 144 is now aligned with an opening 124 in second valve 116and an opening 108 at the second end 120 while first outlet port 142 isaligned with an opening 122 in first valve 114 and opening 106 at firstend 118. As indicated by arrow Q_(C-OUT) in FIGS. 3 and 7, heat transferfluid in working unit 112, now cooled by the MCM, can travel out ofregenerator housing 102 and along line 46 to the first heat exchanger32. At the same time, and as indicated by arrow Q_(C-IN), heat transferfluid from second heat exchanger 34 flows into working unit 112 fromline 50 when working unit 112 is at position 5. Because heat transferfluid from the second heat exchanger 34 is relatively warmer than theMCM in working unit 112 at position 5, the MCM will lose some of itsheat to the heat transfer fluid. The heat transfer fluid now travelsalong line 46 to the first heat exchanger 32 to receive heat and coolthe refrigeration compartment 30.

As regenerator housing 102 is rotated continuously, the above describedprocess of placing each working unit 112 in and out of magnetic field Mis repeated. Additionally, the size of magnetic field M and regeneratorhousing 102 are such that a subset of the plurality of working units 112is within the magnetic field at any given time during rotation.Similarly, a subset of the plurality of working units 112 are outside(or substantially outside) of the magnetic field at any given timeduring rotation. At any given time, there are at least two working units112 through which the heat transfer fluid is flowing while the otherworking units 112 remain in a dwell mode. More specifically, while oneworking unit 112 is losing heat through the flow of heat transfer fluidat position 5, another working unit 112 is receiving heat from theflowing heat transfer fluid at position 1, while all remaining workingunits 112 are in dwell mode. As such, the system can be operatedcontinuously to provide a continuous recirculation of heat transferfluid in heat pump system 52 as working units 112 are each sequentiallyrotated through positions 1 through 8.

As will be understood by one of skill in the art using the teachingsdisclosed herein, the number of working units for housing 102, thenumber of ports in valve 114 and 116, and/or other parameters can bevaried to provide different configurations of heat pump 100 while stillproviding for continuous operation. For example, each valve could beprovided within two inlet ports and two outlet ports so that heattransfer fluid flows through at least four working units 112 at anyparticular point in time. Alternatively, regenerator housing 102, valves122 and 124, and/or seals 136 and 138 could be constructed so that e.g.,at least two working units are in fluid communication with an inlet portand outlet port at any one time. Other configurations may be used aswell.

As stated, working unit 112 includes MCM extending along the axialdirection of flow. The MCM may be constructed from a single stage of MCMalong the axial direction. Alternatively, the MCM may include multipledifferent stages of MCM positioned adjacent to each other along theaxial direction with each having e.g., a different Curie temperature orCurie temperature range over which the MCM in each stage exhibits themagneto caloric effect.

FIG. 9 provides an exemplary plot of a single stage of MCM showing themagneto caloric effect (i.e. a change in temperature, rT, in response toan applied magnetic field of sufficient strength) versus the initialtemperature of the MCM (i.e. the temperature of the MCM upon initialapplication of the magnetic field). As used herein, the original peakCurie temperature, or T_(OC), represents the original initialtemperature (before degradation) at which the MCM shows its peak orhighest temperature change in response to the magnetic field. As usedherein, the original Curie temperature range, or ΔT_(OC), represents theoriginal range of temperatures (before degradation) over which this MCMexhibits a temperature change in response to the magnetic field. Bydefinition, the original Curie temperature range ΔT_(OC) includes theoriginal peak Curie temperature T_(OC).

Appliance 10 and/or heat pump system 52 may be used in an applicationwhere the ambient temperature changes over a substantial temperaturerange. However, as indicated in FIG. 9, a specific stage of MCM mayexhibit the magneto caloric effect over only a much narrower temperaturerange ΔT_(OC). As such, it may be desirable to use multiple stagesconstructed from a variety of MCMs, each having a different originalCurie temperature range ΔT_(OC), in order to accommodate such ambienttemperature changes and to provide the desired temperature to whiche.g., cooling or heating is desired. As such, a given working unit 112might have multiple stages of MCM along the axial direction A toaccommodate the wide range of ambient temperatures over which appliance10 and/or heat pump 100 may be used.

For example, referring now to FIGS. 8 and 10, each working unit 112 canbe provided with stages 152, 154, 156, 158, 160, and 162 of differentMCMs. These stages are positioned adjacent to each other and arearranged sequentially along a predetermined direction—e.g., along axialdirection A-A in this exemplary embodiment. Each such stage includes anMCM that exhibits the magneto caloric effect (before any degradation) ata different original peak Curie temperature T_(OC) or different originalCurie temperature range ΔT_(OC) than an adjacent stage along the axialdirection A-A.

As shown in FIG. 10, the stages can be arranged to that e.g., theoriginal Curie temperature ranges ΔT_(OC) of the plurality of stagesincrease along a predetermined direction such as axial direction A-A.For example, stage 152 may exhibit the magnet caloric effect at originalCurie temperature range ΔT_(OC) that is less than the original Curietemperature range ΔT_(OC) at which stage 154 exhibits the magnet caloriceffect, which may be less than the original Curie temperature rangeΔT_(OC) for stage 156, and so on. Other configurations may be used aswell. By configuring the appropriate number and sequence of stages ofMCM, heat pump 100 can be operated over a substantial range of ambienttemperatures to reach the temperature desired for heating cooling.

In one exemplary embodiment, the original Curie temperature rangesΔT_(OC) of stages 152, 154, 156, 158, 160, and 162 are also selected tooverlap in order to facilitate heat transfer along direction HT. Forexample, in the embodiment shown in FIGS. 8 and 10, stage 162 could havea Curie temperature range ΔT_(OC) of 20° C. to 10° C.; stage 160 couldhave a Curie temperature range ΔT_(OC) of 17.5° C. to 7.5° C.; stage 158could have a Curie temperature range ΔT_(OC) of 15° C. to 5° C.; stage156 could have a Curie temperature range ΔT_(OC) of 12.5° C. to 2.5° C.;stage 154 could have a Curie temperature range ΔT_(OC) of 10° C. to 0°C.; and stage 152 could have a Curie temperature range ΔT_(OC) of 5° C.to −2. These ranges are provided as examples; other Curie temperatureranges may be used as well in still other exemplary embodiments of theinvention.

As previously mentioned, certain types of MCM can degrade during usinguse. More particularly, the original peak Curie temperature T_(OC)and/or original Curie temperature range ΔT_(OC) can change. Thisdegradation occurs when the MCM is held at or near its original peakCurie temperature T_(OC) for long periods of time. By way of example,certain types of MCM containing Lanthanum can undergo such degradation.However, the degradation can be reversed by holding the MCM at atemperature different from the original peak Curie temperature T_(OC).The restoration of the MCM can occur by holding the temperature belowthe original peak Curie temperature T_(OC) or above the original peakCurie temperature T_(OC).

Using working unit 112, FIG. 11 provides an example of degradation ofthe Curie temperature of stage 156. As shown, because stage 156 has beenheld for extended periods of time near at or near its original peakCurie temperature T_(OC-156), the MCM in stage 156 has undergonedegradation such that its Curie temperature has shifted upward (arrow U)to a degraded Curie temperature, T_(OC-156). This results in a gapbetween stages 154 and 158 and may cause heat pump 100 to operateinefficiently or even prevent cooling or heating to the temperaturedesired. Additionally, for this example, only stage 156 is shown asundergoing degradation. However, one or more stages may actually undergosuch degradation.

Accordingly, the present invention relates to restoring the MCM of oneor more stages back to its original peak Curie temperature T_(OC) and/ororiginal Curie temperature range ΔT_(OC) before degradation. Forexample, in one exemplary aspect, the MCM may be restored to withinabout 5 degrees Celsius or less (above or below) of its original peakCurie temperature T_(OC). In another exemplary aspect, the MCM may berestored to within about 2 degrees Celsius or less (above or below) ofits original peak Curie temperature T_(OC).

In another exemplary aspect, the present invention relates to restoringthe MCM of one or more stages to within a certain temperature intervalof adjacent stages. Referring now to FIG. 12, this plot shows theposition of the original peak Curie temperature T_(OC) and originalCurie temperature range ΔT_(OC) for stages 152, 154, and 156 beforedegradation. As shown, dT represents the original peak Curie temperatureinterval between these adjacent stages before degradation occurred. Auniform dT is shown for purposes of example, it being understood thatthe dT between adjacent stages may be not be identical for all stages.The present invention provides for holding the MCM of the stage to berestored at a temperature and for an amount of time that will return thedegraded stage of MCM to within an interval dT of its original peakCurie temperature T_(OC). The interval dT will be measured along thedirection of degradation or i.e., the shift direction of the Curietemperature.

For example, FIG. 13 shows the restoration of stage 156 from itsdegraded Curie temperature T_(DC-156) towards (arrow D) its originalpeak Curie temperature T_(OC). It may not be possible or practical torestore the MCM of stage 156 perfectly to its original peak Curietemperature T_(OC). Accordingly, as shown, the peak Curie temperature ofstage 156 has been shifted back (arrow D) so that restored stage 156 nowhas a restored peak Curie temperature T_(RC-156) that is within theoriginal peak Curie temperature interval dT with stage 158. Moreparticularly, restored peak Curie temperature T_(RC-156) falls withintemperature interval dT of the original peak Curie temperature T_(OC) ofstage 158, which is in the temperature direction (increasingtemperature) of the degradation that occurred for stage 156.

To effect the restoration of a degraded MCM or stage of MCM, the presentinvention provides for holding the MCM at a temperature different fromthe original peak Curie temperature T_(OC). Returning to the heat pumpsystem of FIG. 2 operating in a refrigerator appliance 10 at ambientconditions for example, during normal operation as the heat transferfluid is circulated—one or more stages of MCM in heat pump 100 maydegrade causing a change in the Curie temperature range of the magnetocaloric material away from the original Curie temperature range ΔT_(OC).In order to restore the degraded MCM, a restoration cycle is effected inwhich the operation of pump 42 is slowed to reduce the rate of flow ofheat transfer fluid from a normal operating flow rate. The speed ofrotation of regenerator housing 102 relative to magnetic device 126 mayalso be slowed form a normal rotation rate.

As a result, heat is removed from compartment 30 using first heatexchanger 32. The heat transfer fluid will actually be cooled in firstheat exchanger 32. The cooled fluid will travel by line 44 to exchangeheat energy in pump 100 with the degraded MCM—shifting its temperatureaway from its original peak Curie temperature T_(OC) by cooling thedegraded MCM. This restoration cycle at a lower than normal heattransfer fluid flow rate is continued for a period of time sufficient torestore the degraded MCM as previously described. In an alternativeembodiment, the degraded MCM may be heated to a temperature away fromits original peak Curie temperature T_(OC) in the restoration cycle.

In one example, system 52 is operated so as to maintain the temperatureof the degraded MCM at one or more temperatures that are at least 10degrees Celsius above or below the original peak Curie temperatureT_(OC). In another example, system 52 is operated so as to maintain thetemperature of the degraded MCM at one or more temperatures that are atleast 5 degrees Celsius above or below the original peak Curietemperature T_(OC). In still another example, system 52 is operated soas to maintain the temperature of the degraded MCM above or below (bye.g., heating or cooling) the original Curie temperature range ΔT_(OC).

Once the restoration cycle is complete, the rate of flow of heattransfer fluid can be returned to normal operation. The normal speed ofrotation of housing 102 relative to magnetic device 126 can be resumed.The restoration cycle can be repeated as needed. In one exemplaryembodiment, the restoration cycle could be operated on predeterminedtime intervals to ensure the degraded MCM is restored.

As stated, different types or e.g., alloys of MCMs can have differentCurie temperature ranges over which the MCM will substantially exhibit amagneto caloric effect. In addition, the magnitude of the magnetocaloric effect can also be different for different MCMs. For example,FIG. 14 provides a plot of the amount of temperature change per a unitof material of different MCMs (ΔT/MCM) as a function of operatingtemperature T. As shown, for these particular MCMs, the amount oftemperature change each stage of MCM can provide decreases as thetemperature decreases. Also, the amount of the magneto caloric effectthat can be obtained from a given stage is also dependent upon thestrength—i.e., the amount of magnetic flux—of the magnetic field that isapplied to the MCM. With a given MCM, for example, the magnitude of themagneto caloric effect will be less as the magnitude of the magneticflux decreases.

During operation of a heat pump 100 having stages 152, 154, 156, 158,160, and 162 as shown in FIG. 14, the stages having a higher Curietemperature range become less important as e.g., cooling takes place andthe compartments of the refrigerator approach 0° C. As the temperatureis lowered, the stages having lower Curie temperature ranges (e.g.,stages 152 and 154) provide the cooling required to maintain the desiredtemperature. However, because the stages having a higher Curietemperature range (e.g., 160 and 162) are still being subjected to thefield of changing magnetic flux provided by magnetic device 126 aspreviously described, heat pump 100 is still consuming the power neededto cycle these stages.

Accordingly, as shown in FIG. 8, magnetic device 126 is positionedadjacent to the plurality of stages 152, 154, 156, 158, 160, and 162 andis configured to subject those stages to a magnetic field M ofdecreasing flux along a predetermined direction, which for this exampleis along axial direction A-A. As shown by arrows M in FIG. 8, themagnetic flux decreases as the Curie temperature range associated witheach stage 152 through 162 increases. For this exemplary embodiment,magnetic device 126 can be constructed from one or more magnets.Magnet(s) 126 have a thickness T along a direction O that is orthogonalto the predetermined direction—i.e. axial direction A-A. Moving alongaxial direction A-A, the thickness T of magnet(s) 126 decreases so thatthe corresponding magnetic flux is also decreased along axial directionA.

Other constructions can also be used to provide for a decrease inmagnetic flux. For example, magnetic device 126 may be configured as anelectromagnet or a combination of an electromagnet and one or moremagnets—each of which can be configured to decrease the magnetic fluxalong a predetermined direction.

A variety of configurations can be used to determine the amount or, moreparticularly, the rate of decrease in the magnetic flux provided bymagnetic device 126 along the predetermined direction. For example, inone exemplary embodiment as shown in FIG. 8, the decrease issubstantially linear along axial direction A. The rate or slope of thisdecrease can be matched to the absolute value of the slope of line 127in FIG. 14. In another embodiment, for example, the rate of decreasecould be calculated asRate of decrease=(ΔT/stage 152)−(ΔT/stage 162)/(ΔT/stage 152)  Eqn 1:

Other methods may be used for calculating the rate of decrease as well.In addition, the rate of decrease can also include e.g., a non-linearrate of decrease.

By decreasing the magnetic flux provided by magnetic element 126 asdescribed above, the amount of work associated with cycling workingunits 112 through the magnetic field can be decreased—resulting in moreefficiency in the operation of heat pump 100. In addition, wheremagnetic element 126 is constructed from one or more magnets, the costof manufacturing heat pump 100 and, therefore, appliance 10 can besubstantially reduced.

Returning to FIGS. 4, 5, and 6, for this exemplary embodiment magneticelement 126 is constructed in the shape of an arc from a plurality ofmagnets 130 arranged in a Halbach array. More specifically, magnets 130are arranged so that magnetic device 126 provides a magnetic field Mlocated radially outward of magnetic device 126 and towards regeneratorhousing 102 while minimal or no magnetic field is locatedradially-inward towards the axis of rotation A-A. Magnetic field M maybe aligned in a curve or arc shape. In addition, the thickness T ofmagnetic element decreases along a predetermined direction—axialdirection A-A in this example—as also shown in FIG. 4.

A variety of other configurations may be used as well for magneticdevice 126 and/or its resulting magnetic field. For example, magneticdevice 126 could be constructed from a first plurality of magnetspositioned in cavity 128 in a Halbach array that directs the fieldoutwardly while a second plurality of magnets is positioned radiallyoutward of regenerator housing 102 and arranged to provide a magneticfield that is located radially inward to the regenerator housing 102. Instill another embodiment, magnetic device 128 could be constructed froma plurality of magnets positioned radially outward of regeneratorhousing 102 and arranged to provide a magnetic field that is locatedradially inward towards the regenerator housing 102. Otherconfigurations of magnetic device 128 may be provided as well. Forexample, coils instead of magnets may be used to create the magneticfield desired.

For this exemplary embodiment, the arc created by magnetic device 128provides a magnetic field extending circumferentially about 180 degrees.In still another embodiment, the arc created by magnetic device 128provides a magnetic field extending circumferentially in a range ofabout 170 degrees to about 190 degrees.

A motor 28 is in mechanical communication with regenerator housing 102and provides for rotation of housing 102 about axis A-A. By way ofexample, motor 28 may be connected directly with housing 102 by a shaftor indirectly through a gear box. Other configurations may be used aswell.

In the description above, normal MCM was used to describe the operationof heat pump 100. As will be understood by one of skill in the art usingthe teachings disclosed herein, inverse MCMs could also be used as well.The direction of flow of fluid through heat pump 100 would be reversed,accordingly.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A method of operating a heat pump system, theheat pump system comprising a heat transfer fluid, a first heatexchanger, a second heat exchanger, and magneto caloric material havingan original Curie temperature range, ΔT_(OC), the method comprising:circulating the heat transfer fluid through the first heat exchanger,the second heat exchanger, and the magneto caloric material at a rate offlow; heating the heat transfer fluid flowing through the first heatexchanger during the circulating; cooling the heat transfer fluidflowing through the second heat exchanger during the circulating;reducing the rate of flow of the heat transfer fluid to a lower rate offlow through the first heat exchanger, the second heat exchanger, andthe magneto caloric material after the circulating has caused adegradation such that the magneto caloric material has a Curietemperature range different from the original Curie temperature rangeΔT_(OC); cooling the heat transfer fluid flowing through the first heatexchanger after the reducing; restoring the Curie temperature range ofthe magneto caloric material to the original Curie temperature rangeΔT_(OC); and increasing the rate of flow of the heat transfer fluidafter the restoring.
 2. The method of operating a heat pump system as inclaim 1, wherein the restoring comprises using the heat transfer fluidto heat the magneto caloric material to one or more temperatures abovethe original Curie temperature range ΔT_(OC).
 3. The method of operatinga heat pump system as in claim 1, wherein the restoring comprises usingthe heat transfer fluid to cool the magnetic caloric material to one ormore temperatures below the original Curie temperature range ΔT_(OC). 4.The method of operating a heat pump system as in claim 1, wherein theoriginal Curie temperature range ΔT_(OC) includes an original peak Curietemperature, T_(OC), and wherein the restoring comprises maintaining thetemperature of the magneto caloric material at one or more temperaturesthat are at least 10 degrees Celsius above or below the original peakCurie temperature, T_(OC).
 5. The method of operating a heat pump systemas in claim 1, wherein the original Curie temperature range ΔT_(OC)includes an original peak Curie temperature, T_(OC), and wherein therestoring comprises maintaining the temperature of the magneto caloricmaterial at one or more temperatures that are at least 5 degrees Celsiusabove or below the original peak Curie temperature, T_(OC).
 6. Themethod of operating a heat pump system as in claim 1, wherein theoriginal Curie temperature range ΔT_(OC) includes a peak Curietemperature, T_(CP), and wherein the restoring comprises restoring themagneto caloric material to within 5 degrees Celsius or less of the peakCurie temperature, T_(CP), of the original Curie temperature rangeΔT_(OC).
 7. The method of operating a heat pump system as in claim 1,wherein the original Curie temperature range ΔT_(OC) includes a peakCurie temperature, T_(CP), wherein the restoring comprises restoring themagneto caloric material to within 2 degrees Celsius or less of the peakCurie temperature, T_(CP), of the original Curie temperature rangeΔT_(OC).
 8. The method of operating a heat pump system as in claim 1,further comprising repeating the restoring at predetermined timeintervals.
 9. The method of operating a heat pump system as in claim 1,further comprising transferring heat into a compartment of arefrigerator during the heating the heat transfer fluid flowing throughthe first heat exchanger.